The present invention relates to configuring laser eye protection to accommodate a helmet-mounted display (HMD). More particularly, it relates to selectively admitting desired wavelengths of an HMD in an inner layer while filtering dangerous laser radiation, of similar wavelengths, at an outer layer.
It is desirable to protect the eyes of aircrew from potential exposure to light radiation threats during flight. Such protection (commonly called “laser eye protection” or “LEP”) has traditionally been incorporated into a single visor that is attached to an aircrew helmet. Because it is not feasible to provide LEP for all possible threats, the visor is typically designed to provide LEP for specific threats which are deemed most hazardous, based on the likelihood that the user will encounter the threat and the severity of injury caused by exposure to that threat. The group of wavelength bands for which a particular system provides protection will be referred to herein as an “LEP matrix.”
Conventional LEP systems consist of one or more filter technologies incorporated into a single visor or lens for attenuating wavelength bands in the LEP matrix. Such filter technologies include sputtered dielectric stacks, holograms, polarizing filters, and absorber dyes.
Many modern aircraft also include heads-up display systems (HUD) and/or HMD systems, which provide aircrew with critical data, such as targeting information, aircraft information and enhanced images (e.g., night vision or infrared). Human visual acuity is keenest in the middle of the visible spectrum, which is at a wavelength of about 550 nm. Accordingly, many HUD and HMD display systems use light sources which generate light having wavelength bands that are close to 550 nm (e.g., having peak wavelengths in the range of 525 nm to 560 nm).
In the case of LEP systems which protect against visible threats, a conflict arises between the desire to minimize the intensity of threats that will reach the eyes of the person using the system and avoiding vision impairment on the visible spectrum. This problem is of particular concern for LEP systems in which any of the wavelength bands of the LEP matrix overlaps with one or more of the wavelength bands of the light sources for instrumentation, HUD, and HMD systems. Another problem with conventional LEP systems is that many filter technologies are expensive and/or difficult to incorporate into the large, highly curved visors commonly used on aircrew helmets.
U.S. Pat. No. 5,343,313 to Fergason discloses a helmet having a helmet mounted display system, two polarizing members and a liquid crystal cell located between the polarizing members. Attenuation or blocking of light is achieved by varying rotation of the plane of polarization of light passing through the liquid crystal cell. The HMD system projects onto a surface located between the polarizing members so that operability of the HMD is not impaired by the attenuation of the polarizing members. The eye-protection system disclosed in Fergason has several deficiencies, including an inability to block light threats in specific, narrow wavelength ranges without blocking light in other non-threat wavelength ranges. In addition, the eye protection system of Fergason requires the cooperation of at least three different components to attenuate or block light.
U.S. Pat. No. 5,584,073, to Radzelovage, discloses a helmet system having a display that is projected onto the inside of a visor, where the visor provides laser eye protection.
U.S. Pat. No. 6,411,451, to Fliss, et al., discloses a narrow-bandwidth interference filter in combination with an image intensifier. In Fliss, a filter is placed in front of an image intensifier to provide protection against laser radiation. The image intensifier then amplifies the filtered light to acceptable levels for viewing by the user.
U.S. Pat. No. 6,844,980, to He, describes a HUD or HMD where the reflectivity of a display surface located on the inside surface of a visor can be varied by applying an electrical field to the display surface.